Q:
George Gamow, in his book "The Creation of the universe,"
explained why the galaxies rotate as a solid body as actually
being a "dipping elliptical trajectory" of the stars. So why are
we looking for the missing matter when the "falling" of stars
through galactic gas is more reasonable?

A:
I think Gamow was referring to the inner regions of galaxy. The
outer regions don't rotate as a solid body, which has a constant
angular velocity of rotation. Rather they have a constant linear
velocity of rotation. The angular velocity declines inversely as
the radius.